The present invention relates to a coating composition which is applied to a substrate and contains ultra-fine Tio.sub.2 and to a method for production of the coating composition and to its use.
A coating composition is known from European Patent EP 0 270 472 B1 which contains 24.0 to 35.0% by weight of a thermoplastic or duroplastic resin, 1.1 to 10.5% by weight of a metallic or metallic-like pigment and 1.1 to 10.5% by weight transparent TiO.sub.2 which has a particle size of 20 to 30 nm. The coat composition is intended for use as a base coating for a metallic paint for automobile bodies in the automobile industry. At least one layer of an unpigmented varnish is applied to this base paint. Several layers of a pigmented base paint may also be applied. However, the pigmented coating composition is not used as a top coat. In addition to the metallic effect, the coating composition exhibits the frost effect. The frost effect can be noted when observing coating compositions which contain metallic or metallic-like pigments in combination with finely-divided TiO.sub.2. The frost effect depends on the direction of incidence of the light relative to the sample and to the observer. If the samples are observed from a vertical direction, the coating seems yellowish to golden in color, but if observed from a horizontal direction, the sample looks bluish.
It can be inferred from the publication by J. G. Balfour in J. Oil Colour Chem. Assoc. (1), 1992, page 21 ff. that in the case of paints which contain exclusively ultra-fine TiO.sub.2, the total reflectance of the paints increases with the increase in the pigment volume concentration from 0.1 to 1.0% ultra-fine TiO.sub.2. The increase in the reflectance of the paints is greater in the blue light range at a relatively short wavelength. With the increase in ultra-fine TiO.sub.2 in the pigment volume concentration, the paints appear to be increasingly milky to the observer.
In conventional coating compositions which are applied to a substrate, an improvement in the total reflectance and depth of color is always desired. An improvement in the unsatisfactory stabilization of colored pigments is likewise always desired. This is particularly so when it is necessary to apply preferably only one coating composition as top coat to a substrate, and therefore the total reflectance and the depth of color only result from the one top coat.